WIMBLEDON, Britain -- Top-seeded Novak Djokovic advanced to his 13th consecutive Grand Slam semifinal and maintained his perfect record of not losing a set at this year’s Wimbledon tournament, when he powered his way past No. 7-seeded Tomas Berdych of the Czech Republic, 7-6 (5), 6-4, 6-3, on Wednesday on Court 1.

He will next face No. 8 Juan Martin del Potro of Argentina, who needed medical attention for a knee injury before facing No. 4 David Ferrer of Spain on Center Court but still prevailed, 6-2, 6-4, 7-6 (5).

Del Potro’s left knee was heavily bandaged but he gutted out the win and, like Djokovic, has not lost a set. At the end of the match, Del Potro fell back to the grass and pumped his arms skyward before grabbing his head, almost in disbelief.

“I’m so happy with my level,” said Del Potro, who defeated Djokovic for the bronze medal in the Olympics last summer at Wimbledon. “I beat one of the top players this year.”

Del Potro said he was “really close” to not being able to play and was glad his forehand was a formidable weapon in the match.

“I felt a lot of pain in the beginning of the match,” said Del Potro, who had 12 aces. “It’s really painful. I twist my knee once again but the doctor gave me some magic pills. I’m so glad to go through.”

In the other quarterfinal matchups, No. 2 Andy Murray of Britain was scheduled to play Fernando Verdasco of Spain on Center Court and No. 24 Jerzy Janowicz was to face Lukasz Kubot on Court 1 in the first all-Polish Grand Slam quarterfinal.

Djokovic, the 2011 Wimbledon champion, gained strength as the match progressed. He didn’t convert any of his first four break points in the first set but in the second set came back from being down two breaks and broke Berdych to win the set.

Grunting softly on almost every point, Djokovic fired 16 aces in defeating Berdych for the 14th time in 16 meetings but the first time in two meetings on grass. They previously met on grass in the Wimbledon semifinals in 2010, with Berdych winning, 6-3, 7-6 (9), 6-3.

Djokovic won the first set with a tiebreaker, clinching it after Berdych sent a backhander into the net and then a forehand wide. Berdych broke Djokovic in the first and third games of the second set and held a 3-0 lead, but Djokovic broke back in the fourth and sixth games.

Djokovic easily closed the match out in the third set.

In other tennis news, Roger Federer, who was upset in the second round here, announced Wednesday on Twitter that he will add two events to his schedule. The added tournaments, in Hamburg, Germany, and Gstaad, Switzerland, are played on clay.

“I’ve decided to play #opengstaad. Very excited to play in Switzerland this summer,” he tweeted via his account, @rogerfederer. “This was the event that gave me my first wild card in '98!”